The present invention relates to an optical connector used in an in-vehicle LAN, for example, and, in particular, to an optical connector holding a terminal of an optical fiber cable.
FIG. 1 shows a configuration of an optical connector described in Japanese Patent Application Laid Open No. 2002-131584 (filed on May 9, 2002, hereinafter referred to as Document 1), which is one example of a conventional optical connector of this type. In FIG. 1, reference numeral 11 denotes a housing, 12 denotes a stopper, and 13 denotes an optical fiber cord. The optical fiber cord 13 in this example has a first cladding 13b around the perimeter of an optical fiber 13a and a second cladding 13c around the perimeter of the first cladding 13b. 
A cord hole 14 for containing the optical fiber cord 13 is formed in the housing 11. An opening 15 is formed on one side of the cord hole 14 for allowing the cord hole 14 to communicate with the exterior. A ferrule 16 holding the optical fiber 13a is formed at an end of the housing 11.
The cord hole 14 includes an entrance hole part 14a and cord holding hole part 14b. A fiber holding hole 16a formed in the ferrule 16 is positioned forward of the cord holding hole part 14b. Reference numeral 17 in FIG. 1 indicates a mating piece to be mated to another optical connector.
The optical fiber cord 13 is inserted through a back end of the cord hole 14, the second cladding 13c is placed in the entrance hole part 14a, and the first cladding 13b is placed in the cord holding hole part 14b. The optical fiber 13a is placed in the fiber holding hole 16a in the ferrule 16. In this state, the stopper 12 is inserted through the opening 15 in the direction orthogonal to the direction in which the optical fiber cord 13 is inserted. As a result, a pair of holding plates 12a of the stopper 12 in each of which a U-shaped slit (not shown in FIG. 1) is formed are engaged in (enter) the first cladding 13b of the optical fiber cord 13. Thus, the stopper 12 positions and fixes the optical fiber cord 13 in the direction of the axis of the optical fiber cord 13.
FIG. 2 shows a configuration of an optical connector disclosed in Japanese Patent Application Laid Open No. 2001-51156 (filed on Feb. 23, 2001, hereinafter referred to as Document 2). An optical connector 20 holding an optical fiber is mated to another optical connector 30 holding a photonic device module in FIG. 2.
The optical connector 20 includes a ferrule assembly 21, a housing 22, a spring cap 23, and a spring 24. The ferrule assembly 21 consists of an optical fiber 25 and a ferrule 26 which is attached to the terminal of the optical fiber 25 passing through the spring 24. The ferrule 26 includes a small diameter part 26a and a large diameter part 26b. A flange 26c is formed in the large diameter part 26b. One end of the spring 24 abuts on the flange 26c. 
A chamber 22a accommodating the ferrule assembly 21 is formed in the housing 22 and a stopper 22b is formed in the middle of the chamber 22a. An engage hole 22c is formed in the rear sidewall. A fiber leading part 23a is formed in the spring cap 23 so that the optical fiber 25 can be held. A locking protrusion 23b that engages in the engage hole 22c of the housing 22 is formed on the front end external surface of the fiber leading part 23a. The rear end face 26d of the ferrule 26 and the other end of the spring 24 abut on the front end of the fiber leading part 23a. 
The optical connector 20 is assembled by inserting the ferrule assembly 21 from the rear of the housing 22, then passing the optical fiber 25 through the fiber leading part 23a, and fitting the spring cap 23 in the rear of the housing 22.
In an optical connector of this type, it is important to ensure a sufficient pull-out strength so that the optical fiber is not pulled out from the optical connector when an accidental force (pull force) is applied to the optical fiber. In addition, if the optical fiber excessively moves in the direction of the axis of the optical fiber when the optical fiber is pulled, connection loss increases. Therefore, the optical fiber needs to be prevented from being excessively displaced under a pull force.
The conventional optical connector shown in FIG. 1 retains the optical fiber cord 13 so as not to be pulled out by merely digging the stopper 12 into the cladding 13b of the optical fiber cord 13. Therefore, if the optical fiber cord 13 is strongly pulled, the retention can loosen and the optical fiber cord 13 can be significantly moved in its axis direction.
In the conventional optical connector shown in FIG. 2 on the other hand, the rear end face 26d of the ferrule 26 holding the optical fiber 25 abuts on the spring cap 23 to restrict an excessive displacement of the optical fiber 25 when the optical fiber 25 is pulled. However, the spring cap 23 is attached to the housing 22 only by the locking protrusion 23b merely engaging in the engage hole 22c of the housing 22. Therefore, when the optical fiber 25 is strongly pulled, for example, the excessive force can damage the engaging part (the locking protrusion 23b and the engage hole 22c). As a result, the optical fiber 25 (the ferrule assembly 21) can be pulled out.